Could I be venting the radiator too quickly?

Captain Who

Exactly. The steam and air mix somewhat at the boundary layer and the vents do not just snap closed the moment the last bit of air is gone. That's why any charts done at an ambient temp. will somewhat underestimate the time it will take for the same amount of air to be expelled in a steam system. As the orifice gets smaller the CFM rating of the vent decreases.

Fred

Hatterasguy said:

Fred said:

Those vents aren't metered in any way. They will take whatever air is given them, up to the capacity of the ports on them. They are wide open until the steam starts to close them.

Those vents deliver air proportionally based on pressure. They are not wide open.

It's only proportional because varying pressures are required to support the push it takes to move that air at any given rate, not because of anything in the vent itself. That is driven by the source of the pressure, not the vent. They are wide open when cool and the venting is hindered, at some point when the temp gets high enough to start activation of the bimetal or heats the alcohol (in the case of Hoffmans) enough to start to raise the float. The only functional part of those vents is the mechinism that is sensitive to heat.

Fred

"If this were the situation, they would vent the same amount of air at 1 ounce and at 2 ounces and at 3 ounces as the rate of the open port."
Not correct. There is no pressure sensitive restriction inside them. As long as the port(s) on top can support the air output, pressure is the only thing that drives the volume. There is a point (and I don't know what it is) where the port capacity will restrict how much air can be pushed out at any pressure.

Fred

Hatterasguy said:

Of course it is correct, Fred. The flow rate through the vent is identical to the flow rate through the open port if there is no restriction in the vent.

Look at the charts. The venting rate of the Gorton #2 is significantly less than the venting rate of the open port.

The only conclusion that can be made is that the Gorton #2 is restrictive.

We're probably splitting hairs here. The flow rate out of a .5" or 3/4" pipe is always going to be greater than out of a vent that has a couple 1/8" ports. My only point is, , based on your calculation above, if 1/4 ounce of pressure will deliver about 1.5 cubic feet of air per minute, out of a 3/4 inch hole, thats all the air available to vent and that may be the optimum venting for that main (different size vent pipe, different vent requirements obviously) and the 1 Gorton #2 per 20 feet of 2" pipe or 12feet of 2.5" pipe is probably not valid because there is not enough pressure at boiler start up to drive the volume of air to the levels that the vent pipe and vents could accommodate if the pressure were there.
I understand the vents close at some rate and that is a restriction but that assumption is already built into the tables that show the vent rates for the various vents.
For example, 5 Gorton #2's could empty this 80 ft. 2" main (2.4 Cubic feet of air) out in about 30 seconds if he could get 1 Oz of pressure out of the gate. (or 1 oz. of vacuum on the backside of the vent), using the vent charts, with the closing rate already built in. No?
Maybe we need to start a thread to discuss putting a small vacuum pump on the end of the main that would power up on initial burner start-up and power down on a temp setting at the end of the main.

Fred

Hatterasguy said:

Fred said:

We're probably splitting hairs here. The flow rate out of a .5" or 3/4" pipe is always going to be greater than out of a vent that has a couple 1/8" ports. My only point is, , based on your calculation above, if 1/4 ounce of pressure will deliver about 1.5 cubic feet of air per minute, out of a 3/4 inch hole, thats all the air available to vent and that may be the optimum venting for that main (different size vent pipe, different vent requirements obviously) and the 1 Gorton #2 per 20 feet of 2" pipe or 12feet of 2.5" pipe is probably not valid because there is not enough pressure at boiler start up to drive the volume of air to the levels that the vent pipe and vents could accommodate if the pressure were there.
I understand the vents close at some rate and that is a restriction but that assumption is already built into the tables that show the vent rates for the various vents.
For example, 5 Gorton #2's could empty this 80 ft. 2" main (2.4 Cubic feet of air) out in about 30 seconds if he could get 1 Oz of pressure out of the gate. (or 1 oz. of vacuum on the backside of the vent), using the vent charts, with the closing rate already built in. No?
Maybe we need to start a thread to discuss putting a small vacuum pump on the end of the main that would power up on initial burner start-up and power down on a temp setting at the end of the main.

We are not splitting hairs. This is a fundamental distinction in the physics of these vents.

You mentioned above, and I agree, that you only have the capability of venting about 1.5 CFM through an open 3/4" port at .25 ounces/square inch.

Now, if the Gorton #2 is completely not restrictive, when you add it to the pipe, the venting rate will remain exactly the same.............25 ounces/square inch.

But, sadly, this is not the situation. The Gorton #2, due to the 1/8" opening for discharge, provides an additional restriction. My completely uneducated guess is that this vent will deliver .25 CFM at .25 ounces/square inch.

Note that this flow rate is much less than the open 3/4" port at the same pressure.

Five #2's will probably empty this main in a bit over two minutes IF the pressure is .25 ounces/square inch.

I can tell you that on my own system, I do not have .25 ounces/square inch for the first 10 minutes. The needle does not move off the peg. This is a 20 ounce/square inch gauge full range.

So, all of the discussions on how many vents are required must be anecdotal because the tables are wildly above the actual venting rate available at startup.

Agreed, when all is said and done, vent rate tables should reflect real word conditions at boiler start up with minimal pressures.
I am still looking at the tables that say at 3 oz. of pressure, a 3/4 inch pipe will vent 9.5 cubic feet of air per minute and a Gorton #2 will vent 2.2 cubic feet and it has a 1/8 inch port (about 1/6 the size of a 3/4 inch pipe). I continue to maintain the only restriction is the port size on the top of the vent.
This link shows the interior construction:
http://www.gorton-valves.com/products

Two moving parts, the bi-metal actuator and the vent steam valve that is lifted by the bi-metal actuator to close the port.

jch1

Thank you all for your insights. Where does this leave me as far as my venting strategy goes?

Captain Who

I like to think of it in terms of the boiler's evaporation rate, rather than pressure. Pressure is simply a by-product of the overall restriction that the steam sees on it's journey to wherever it is headed. That restriction is a varying factor due to the fact that the orifice of the vents is getting smaller as the vent heats up. A larger boiler, due to the higher evaporation rate, will produce a higher pressure at any given moment with a given system total restriction (length and diam of pipes, orifice area of vents). Anyone who has taken some fluid mechanics or has experimented with carburetors knows that a smaller orifice can discharge less of a fluid or gas when it is exposed to a given pressure drop. In a carburetor that pressure drop is the difference between the pressure in the float bowl (atmospheric pressure) and the pressure at the venturi (a function of air mass flow rate and venturi cross sectional area reduction). Everyone knows that a smaller jet produces a leaner mixture.

Thinking of it all this way just keeps it clearer in my mind. Its very simple.

nicholas bonham-carter

Remember that you are really aiming for a balance between the back-pressure of the main vents, and those of the radiator vents. If the restriction, of the main vents, as measured by back-pressure is greater than than the total of the radiator vents, then the runouts to the radiators closest to the boiler will start to fill with steam sooner than those at the end of the line, giving an unbalanced steam distribution. This becomes even more important when you have more than one main.
If you had an IR camera, this would be more easily seen.
If someone can come up with the affordable, and reliable,electric vent, this could be one of the greatest developments in the history of one pipe steam.
Maybe traps could be replaced by this as well.--NBC

Mark N

Jch1, I don't know how much research you've done on your venting. At the top of the Strictly Steam section is a thread labeled "Before you Ask". There are 2 links there. One is for the "Heating Museum". Next find "Old Steam", then look for the following articles. "Controlled Air-Venting of One-Pipe Steam Systems", "It's All in the VENTING", and "The Big Fault in One-Pipe Heating". I would recommend printing out and reading these articles. There is much to learn when you wander off the Wall.

PS I would also recommend that you read "Piping design for Oil Firing"

jch1

Thanks for the information. I would say that I've figured most of this out through frequenting the wall, but still informative, nonetheless.

I'll reipe the vent stack in the next few days. In other news, I raised the radiator that was noisy, and I think that eliminated the problem. I can't be sure just yet because it's been pretty warm here over the weekend.

jch1

Here's an update. I replaced the antler with all .75'' fittings and used reducing tees and a reducing elbow. With the three Gortons attached, but the top of the first tee open I timed 5:30 minutes to get steam to the end of the main. This is 45 seconds faster than the previous setup with the first tee being a reducing one to 0.5". I'll time it with this setup tomorrow. Thoughts?

nicholas bonham-carter

What a big improvement!--NBC

jch1

Sorry, I need to take a step back. First, this is the first time that I timed my system with a completely open vent pipe. So the 6:15 mark was actually with all four vents connected and the fittings reducing to 0.5". I still need to time it with all four vents attached and on the 0.75" fittings. I'm guessing it will be somewhere around 6 minutes. Attached is a picture with the current configuration.

jch1

Alright, I've got another update. I'll provide a recap here as well.

At the end of my approx. 80" main (it's one large loop around my basement) and at the end of my dry return is a 3/4" tapping. I put a 4" nipple on that, to a 1/2" reducing tee (two branches 1/2", the other was 3/4"), and had 1/2" nipples, tees, and elbows for three Gorton 2s and a Hoffman 75. I timed how long it took for steam to reach the header to the end of the return, just before reaching the vent stack. I times this to be 7 minutes, 51 seconds.

Next, I was told to measure how long it took steam to get to the dry return, to a point just after the last radiator tee on the main. I waited 3-5 hours, and timed the same setup again and came up with 6 minutes, 16 seconds. I'm thinking the system was a bit warmer this time, but I can't verify this.

Next, I was told to replace the 1/2" fittings with 3/4". With that, I replaced the tee off of the initial 3/4" nipple with a 3/4" one, used 3/4" nipples the entire way across, and 3/4" x 3/4" x 1/2" reducing tees, so the only thing that's 1/2" are the branches directly feeding the vents. Time to re-time:

3 Gorton 2s, no Hoffman 75 (one of the branches of the very first tee is empty, leaving an open system): 5 minutes, 30 seconds.

I just re-timed everything, with 3 Gorton 2s and the Hoffman 75: 6 minutes, 10 seconds.

Summarizing, it looks like an open system gives me 5' 30", 3/4" closed system gives me 6' 10", 1/2" closed system gives me 6' 16". Interestingly, it doesn't seem like there's really an appreciable difference between 3/4" and 1/2" fittings, and I'm not sure that I want to spend another x dollars for another Gorton 2. I plan on measuring everything again with one of the Gorton 2s removed and the fitting plugged. Interested in seeing if it's worth it.

Another interesting note is that I stayed down by the boiler the entire time it was on, going from 68 degrees to 72 degrees. Thanks to my ecobee thermostat, I can obtain some pretty interesting info. I turned on the system at 7:19pm, and my system didn't read 1oz of pressure until 8:03pm (visually saw this on my 0-3 psi pressure gauge). As I was observing the pressure rise, my system suddenly shut off. I wasn't sure if it was an issue with my pressuretrol or lwco, but everything looked fine, but my temperature was not yet at 72 degrees. 10-15 minutes later, I realized that my temperature has increased to 72 degrees, so it seems as if the thermostat knows when to shut off the boiler in anticipation of arriving at my desired temperature. 50ish minutes seems pretty good for a temperature rise of 4 degrees, yeah?

I had one question. I felt my radiators, and some only had 2-3 sections warm, but others were entirely warm. This got me thinking that I need to just put a different vent on that radiator. What would happen if I put all faster venting vents on my radiators (making subtle variations to properly balance everything), thus allowing the system to heat up faster? Is this not preferred over having all slower venting radiators? I'm referring to having a system with, assuming they are reliable, all vari-valves open medium-to-wide to allow the radiators to heat up faster than, say, Hoffman 40s and ventrites.

I know I wrote a lot, but I'd appreciate any thoughts.

BobC

I would use the smallest vents that allow all the radiators to heat at an equal rate. If you start venting the radiators too fast you will probably unbalance the system.

You may have to diddle with this somewhat so it gives you good even heat on really cold days.

Bob

Captain Who

Assuming all the radiators were properly sized for the rooms they are in, you definitely need to balance them all so that their vents close around the same time. You are already venting your mains about as fast as you can which is good. If the rest of the system were all perfectly insulated and there were no heat being lost up the flue you could have the luxury of venting all the radiators super slow so that the vents are nice and quiet and the radiators are quiet, but that is not the case. Therefore you want to vent the radiators as fast as you can without having too much noises. That's the way I have my system working and I'm happy with it. I don't think they are the best in all respects but I'm mostly using varivalves which have quite a large venting capacity. They are of course adjusted differently on each radiator.

jch1

Right, I need to insulate my mains and figure out what to do with the finished portion of my basement that uses the main to provide heat. With that, I'm having trouble determining what would happen if I used fast radiator vents (assuming they were properly balanced to close at the same time). Wouldn't that result in the radiators warming up a bit quicker? Is the only "harm" involved just having a few noisy radiators?

Captain Who

Well it's not just noise. If the condensate is formed too fast for the ability of the system to let it drain back, it will impede the flow of steam into the radiator, which is noisy, but it also will harm efficiency. That's why it's crucial to have the proper pitch on the radiators and supply runners. I think I have exceeded the recommendations because I think of them as a bare minimum, especially with an old system that can have sediment buildup. In some problem radiators I had to actually reverse flush both them and their supply runners with water to get everything working properly. That has to be done carefully to avoid pushing sediment and crud back into the boiler though.

jch1

Aaah that's interesting, and what I needed to know. So venting "fast" is okay so long as it isn't too fast to create problems. Would it be harmful to just raise all of my radiators a bit (say a quarter of an inch) while ensuring they remain properly pitched? I know this may seem weird, but I'm excited to know that I'm getting close to a much more solid system.

Captain Who

Ha ha it's not weird at all (I hope:)). Raising the radiators a little more shouldn't hurt, providing it doesn't strain any fragile pipes. You'll probably be just compensating for sag in the house that has occurred over time though. You can't balance the system perfectly for all percentages of radiator fill, so you will have to find the right tweak for your average operating conditions. A good place to start is to get them balanced at 100% fill and work from there, since that isn't a typical condition unless you do a setback every night like I do. You will see some major efficiency benefits and quietness benefits when you insulate everything really well.

jch1

I do in fact do a minor setback of 3-4 degrees at night and when we leave for the morning. I'm happy to say that I haven't heard any major clanking or anything since I raised that one rad.

My next step is to attempt to increase the vent rate of all the rads in my system slightly so as to get things to heat a bit faster.

Mark N

If you increase the venting on all rads relative to each other, it most likely wont heat up faster. You're still producing the same amount of steam.

jch1

Hmm. So let's assume I had five radiators which all used Hoffman 40s and they were properly balanced with the Hoffman 40s. If I switched out these five Hoffman 40s for ventrite #1s (or hoffman 1a, or Gorton 4, 5, 6, C, etc.) and set all of them at the same vent rate, the radiators wouldn't heat up faster than they did with Hoffman 40s? Could you explain why they wouldn't?

jch1

Mark N, I just noticed you said "relative to each other". What I'm suggesting is maintaining the venting proportions relative to each other, but simply increasing the values. So for example, if I had one vent that was set at 2 times that of another, I'd maintain that proportion but increase the vent rate of both. I hope that makes sense?

KC_Jones

Your boiler makes steam at a fixed rate. Unless you are building a lot of pressure and/or cutting out on pressure you won't really heat any faster with bigger vents. Bigger vents won't make more steam. Now if you are building pressure in the system then you could possibly heat faster, but going too fast also runs the risk of overshooting and spitting vents.

Captain Who

The boiler makes steam at a fixed rate as far as BTUs go. Every minute that it is operating you are losing some heat up the flue and through the supply pipes to the radiators. The ultimate goal is to lose heat through the radiators into the room when the steam condenses there. So why not try to get the steam into the radiators with as little restriction to flow as possible, without getting negative issues like spitting vents or condensate blockages? Makes sense to me, if you are trying to maximize efficiency. As far as overshoot goes, I don't believe that is an issue because modern digital thermostats monitor that on every cycle and make anticipation adjustments as needed to control that.

jch1

Right, I get that the boiler makes steam at a fixed rate. So let's say, based on my calculations, that steam hits the main/dry return (the point just after the take off for my last radiator in the loop) at 6.25 minutes. I now have to get steam to the radiators. Similar to with my main venting, why not try to do this as fast as possible by using faster vents? I think this is what Captain Who seems to be suggesting as well.

Alternatively, are you suggesting that because my system operates at a low pressure (just barely saw 1oz after an hour, and the system shut off shortly thereafter because I reached my set point of 4 degrees higher), having larger vents on the radiator is of no consequence because the steam will still be moving towards my radiators at a slow pace corresponding to the <1oz pressure?

I think I may be overthinking things at this point. Help!

Fred

My opinion is, since your boiler pressure is so low (which is a good thing), putting larger vents on the radiators will probably cause them to warm faster but they won't reach capacity any faster because you are currently using all the steam the boiler can (or is) producing. End result is the heat may feel more gradual and comfortable on the front end of the cycle.

RomanGK_26986764589

I have one main and it is about 70 ft long. 2" pipe. it takes 4 minutes for it to heat up.

nicholas bonham-carter

That seems acceptable. However the best way of knowing if your main venting is doing its job would be to have a low pressure gauge, in ounces. The resistance to the escaping air is the back-pressure, seen on the gauge as the boiler begins to make steam.
To add something to the ancient post above, the back-pressure of the main vents must be lower than the back-pressure of the rad vents. This will achieve a balanced system where all rads receive steam at the same time.
This is hard to measure without closing one set of vents-rad and firing the boiler, and noting the value. Then with the main vents removed, and ports plugged, and rad vents opened, firing the boiler again and comparing the pressures. If all the rad vents were oversized, then the steam would arrive at radiators closest to the boiler first followed in turn by the others further away. This would be an unbalanced system, which is why we say, "vent the mains fast, and the rads slowly.--NBC

ChrisJ

Here's a diagram of my venting.
I run at 0.25 to 0.5" WC which is 1/4 to 1/2 an ounce.










Some radiators have Gorton 4s while others have Cs. It all takes time to balance and figure out when running such low pressure. I run at 2 cycles per hour and the system is very well balanced. One thing I would do is dump the varivalves though.



By the way, did you ever get the knocking taken care of? If not, are you sure it's hammering and not just rubbing noises from thermal expansion of the pipe?

jch1

Hey all- I haven't really been back on the wall besides helping people with the conversion from the CycleGard to Safgard. Funny to see this post revive itself because I was considering removing the two remaining varivalves and putting on adjustable ventrites in their place, primarily because there are one or two radiators which aren't getting anywhere near as much heat (they have Hoffman 40s on them). I figure with a complete system of Ventrite #1s, I can really fine tune things. Thoughts?

@ChrisJ it's funny you mention the knocking, because in some rooms it is better and in others it is substantially worse. I put one radiator that was the main troublemaker on wooden risers on every leg of the radiator, and it interestingly seems to tap for about twice as long now. With that being said, I'm fairly confident that the noise is coming from a wall which houses the pipe because the wall actually gets warm. I don't think it's worth my time to open up the wall to figure it out.

The biggest "problem" I have is actually a different radiator which was replaced due to a cracked section in the old one. This radiator actually bangs or moves substantially after a period of time, to the point that I can feel the movement when i'm in that room. It only happens once per cycle. I know it's moving or lurching because the replacement radiator is taller than the old one, so the cover doesn't sit on the ground all the way. When it moves, the cover very visibly moves as well. Thoughts there?

Sorry for the long comment. I think what I'll eventually try is slightly raising all of the rads to see if there's any remaining water anywhere. I also think I have a leak somewhere because my LWCO activated after about a month of use late last year.

ChrisJ

Steam pipes and radiators expand as they heat and contract as they cool. If the pipe rubs on wood it can make a popping sound as it gets stuck and then springs free repeatedly. This often sounds like a popping sound and can be pretty loud. My first step would be to check the clearance of the floor around the pipe, there should be a gap. If it's rubbing on one side try putting a piece of plastic milk carton in between the wood and the pipe and see if it helps. I've done this on a few of mine and it makes them silent.

Same thing can happen if it rubs against other things such as pipe hangers.